In the drilling of oil wells it is often desirable and sometimes required to sever and recover the well casing. In marine drilling the submarine well head equipment is very expensive and when the well is abandoned it can be recovered by severing the casings in the well bore and retrieving the severed casings and well head equipment. Also in some locations, the submarine well head equipment and a portion of its casing must be recovered to assume that they do not become a hazard to navigation.
Prior to my present invention, there have been many casing cutters which are adapted to be lowered into a well bore and to sever the casing cemented therein. The Sanford, U.S. Pat. No. 3,331,439 discloses one form of such cutter. This general type of casing cutter is illustrated in the drawings of the present application as a sample of the prior art. Such patent discloses a cutter having arms that pivot outwardly from a point mounted on the body of the cutter and are of sufficient length so that they can move outward to cut the outermost casing which they will encounter. In doing so, such blades cut a very substantial portion of the innermost casing and much of the cement between the casings before finally severing the outermost casing.
Another structure of the prior art is disclosed in the Kinzbach, U.S. Pat. Nos. 2,322,695 and 2,322,694. Such devices have arcuate cutting blades adapted to move outward but such cutters are not capable of cutting a large diameter swath as through a plurality of surrounding (concentric or eccentric) casings. The present invention relates to an improved casing cutter for use in a well bore which is capable of severing a plurality of casings with a minimum removal of casing material and the cement between the casings. Such cutter, by use of improved guide means, translates part of the longitudinal force produced responsive to the circulation of fluids downwardly through the drill string into a radially outward extension of a plurality of arcuate blades. Upon rotation of the tool, such blades cut a very narrow swath through the casing and cement between the casings so that they remove substantially only the amount of material to allow the swath to have the shape of the blade.
The movement of each blade relative to the body of the tool is in a path which is generally arcuate in a longitudinal plane. Guide means cooperative between the tool body and the blade are provided to guide the blade in this arcuate path. The guide means are disposed so that they will not unduly limit the downward movement of the actuating mechanism so that the the blades may be extended outwardly of the body over the major portion of their lengths. This allows a relatively large diameter swath to be cut without using excessively long blades.
An object of the present invention is to provide an improved casing cutter for use in a well which is adapted to sever multiple surrounding casings with a minimum amount of cutting and removal of material.
Another object is to provide an improved well casing cutter which will sever multiple casings within the well bore with a minimum amount of wear on the cutter blades.